Detection of the level of the metal bath in the moulds for continuous casting



Aug. 5, 1969 p, PONCET 3,459,949

DETECTION OF THE LEVEL OF THE METAL BATH IN THE MOULDS FOR CONTINUOUSCASTING Filed Dec. 1, 1964 2. Sheets-Sheet 1 ATTORNEY Aug. 5, 1969 PPQNCET 3,459,949

DETECTION OF THE LEVEL OF THE METAL BATH IN THE MOULDS FOR CONTINUOUSCASTING Filed Dec. 1. 1964 1 2 Sheets-Sheet 2 l M01. raw LEVEL H IGHT Iflea-H126 CELL RESPOAASE Gm, 913? BY vm M A I :1 ORNEB ABSTRACT OF THEDISCLOSURE In the photo-electric detection of level variations withinthe mould of a continuous casting machine, there is formed an opticalimage of the upper surface of the molten bath within the mould, as forinstance by means of an objective lens, and the cell is disposed on aspot of this image, as far as possible from the image of the jetofmolten metal flowing into the mould, so as to be exclusively influencedby level variations ahd not by the jet itself.

This invention relates to the continuous casting of metals by means of agenerally water-cooled mould into one end of which the molten metal ispoured, while the solidified bar thus obtained is continuously withdrawnfrom the other end thereof.

One of the problems with which such a process is com cerned consists inmaintaining the molten metal at a sub stantially constant level in .themould by acting either on the rate of flow of the molten metal into themould, or on the linear velocity of the solidified bar issuingtherefrom. This adjustment is generally effected manually and ittherefore requires the presence of a skilled operator in the vicinity ofthemould for detecting any substantial variation of the liquid leveltherein.

Several methods have been proposed for detecting these variations andfor automatically effecting the corrections required. In one knownembodiment a radiation pyrometer is disposed obliquely with respect tothe mould in such manner that the intensity of heat energy which itreceives depend upon the height of the level in the mould, the signalfrom the said pyrometer being used to actuate the correcting orregulating mechanism. The disadvantage of this known arrangement is thatthe pyrometer is in fiuenced not only by the surface of the bath ofmolten liquid in the mould, but also by a number of other heatemittingbodies, and primarily by the jet or stream which flows into the mouldfrom the tundish or other liquid metal container. Since this jet orstream is at a substan tially higher temperature than the bath which iscooled by the mould wall, its undesirable influence is considerable. Itis the object of the present invention to avoid this disadvantage.

In accordance with the present invention a method for the detection ofthe variation of the level of the bath of. molten metal in the mould ofa continuous casting unit consists in forming an optical image of thesurface of the bath within the mould by means of an objective lens orthe like having its axis disposed obliquely with respect to the verticalaxis of the mould inlet, and in so disposing at least one detectingphoto-electric cell on a small sur=- face of the said image situated farfrom the image of the liquid jet which flows into the mould, that thesaid detecting cell be responsive to the variations of the said levelabove and below an average level corresponding to the desired normallevel without being substantially influenced. by the jet itself.

In a first embodiment of the invention a single detect ing cell isdisposed on the line which delimits the surface, of the bath within themould in the optical image when a. mg a the level of the said bathcorresponds to the normal levelv desired.

Alternatively a plurality of detecting cells are disposed on the linewhich delimits the surface of the bath within the mould in the opticalimage when the level of the said bath corresponds to the normal level.desired, the response of the said detecting cells being additive.

According to another feature of this invention a first group of at leastone detecting cell is disposed on a line which delimits the surface ofthe bath within the mould in the optical image when the level of thebath is below the normal level desired, while a'second group of at leastone detecting cell is disposed on a line which delimits the said surfacein the said image When the level is above the normal level desired, theresponses of all these de tecting cells being additive.

An auxiliary reference cell map further be so arranged as to detect thevariations of external conditions, such as the temperature of the moltenmetal poured into the mould, which could influence the detecting cell orcells, without being itself influenced by the level variations in themould, the response of the said reference cell, or a fraction thereof,being substracted from the response of the detecting cell or cells.

The auxiliary reference cell may be so disposed as to see the jet ofhigh temperature liquid metal which flows into the mould, substantiallywhere this jet issues from the pouring tundish and it may for thispurpose be dis posed behind an auxiliary objective lens.

In the accompanying drawings:

FIG. 1 is "a diagrammatical illustration of a continu ous casting unitequipped with a detecting arrangement: according to this invention.

FIG. 2 shows the optical image formed by the objective lens of thisarrangement.

FIG. 3 is; the graphic representation cell response versus molten levelheight in the arrangement of FIGS. 1 and 2.

FIG. 4 is a view similar to FIG. 2 but corresponding to an embodimentcomprising a pair of cells responsive to the same level line in theoptical image.

FIG. 5 is a view similar to FIG. 1, but corresponding to the embodimentillustrated in FIG. 2.

FIG. 6 illustrates the optical image in an embodiment comprising twopairs of cells, each pair being responsive to a predetermined levelline,

FIG. 7 is the corresponding graphic representation response versus levelheight.

FIG. 8 shows the optical image in the case of three pairs of cellsresponsive to three different level lines.

FIG. 9 is the block diagram of a regulating device.

FIG. 10 diagrammatically shows a continuous casting unit with adetecting arrangement comprising a reference cell.

FIG. 11 shows a possible mode of connection of the reference cell in theregulating device.

In. FIG. 1 the molten metal 1 from a tundish 2 flows in the form of ajet or stream 3 into the upper end of a vertical water-cooled tubularmould 4 where it forms a liquid bath 5, while the solidified bar 6 ispulled from the lower end of the mould at a substantially uniformvelocity. The flow rate is controlled by a conical refrac tory block orvalve 7 actuated by a rod and lever gearing 8, 9, in order to maintain asubstantially constant level in the mould. Alternatively the block orvalve 7 may be dispensed with the control of the level in the mouldbeing affected by variation of the linear velocity of the solidi tiedbar 6.

An objective lens 10 is laterally disposed at an angle to the verticalaxis of the mould, so as to form an. inverted optical image of the upperend thereof together with the low r portion of the liquid. iet and theupper surface. oi":

the molten metal bath 5, the whole as clearly shown FIG. 2. This imagecould be observed for instance on a ground glass disposed in a plane 11transverse to the .axis of the lens. A photo-electric cell 12 issituated in the plane 11, in-the optical image of the bath '5, at a dis=tance from the image of the jet 3 and substantially on the line A, ornormal level line, which limits the surface of the moten metal bath inthe optical image of'FIG. 2 when the level is normal in the mould.

Considering FIG. '3 in which the adscissae represent the height of themolten metal level in the mould while the ordinates correspond to theresponse of the cell, when the level is low (line A in FIG. 2) theenergy received by the cell is reduced and consequently its response(vo1tage, intensity or resistance) is small. When the level rises, thecorresponding level line moves downwardly in FIG. 2 and when itapproaches position A, the cell begins be ing illuminated. lts responserises rapidly until it is fully illuminated, the said responsethereafter remaining substantially constant. It is seen that thegradient of the cell response is quite substantial between abscissae aand b. The response of the cell may thus be used for the auto maticactuation of the block or valve 7 in order to maintain the molten metallevel at a substantially constant height close to the normal level. lineA.

The cell is small with respect to the optical image and owing to itseccentric position therein, as indicated in FIG. 2., the said cell issubstantially unaffected by the image of the bright jet 3 which it doesnot see. Even if this jet moves somewhat to and fro, as this mostfrequently occurs, its image will generally not reach the cell and causea false response thereof.

The photo-electric cell 12.- is preferably selectively sen sitive toinfra-red. It is thus practically unaffected by the flames of the gasburners which are generally used to protect the molten metal fromoxidation.

In FIG. 4 the cell has been duplicated, in this sense that twoindividual cells 12a, 12b are disposed on the normal, level line A, oneon each side of the image of the jet 3. These cells are so mountedelectrically with re spect to each other (as for instance in series orin parallel according to their characteristics) that their responses beadditive. If one of them is incidentally influenced by the jet during anabnormally large lateral displacement thereof, the undesirable effect onthe final response will only be one half of what would have been thecase with the arrangement of FIG. 2.

In FIGS. 5 and 6 the level detecting arrangement comprises two pairs ofcells, each pair being arranged as in FIG. 4, apart from the fact thatone pair 112a, 112b is substantially disposed on a low level line A andthe other pair 212a, 212b on a high level line A". FIG. 7 shows thegraphic representation response versus level height respectively for theset 112a-112b and for the set 212a 21%. The curve in dash linerepresents the total or addi tive response, as for instance if bothpairs are connected in series in the case of voltage emitting cells. Itwill be observed that the response gradient extends through a distanceor height c-d which is much greater than in the case of FIG. 3. Theautomatic detection is therefore more progressive. It is obvious thatone cell could be omitted in each pair. More particularly thearrangement could only comprise two cells, such as 112a and 212a,disposed on the same side of the jet. In such a case if the latterdeviates towards the said side it influences both cells and thereforethe resulting disturbance may he re duced to a minimum.

FIG. 8 illustrates an arrangement comprising three pairs of cellsIna-112b, 212a-212b and 312a-312b, the latter being disposed on thenormal level line A. The response of the detecting unit is still moreprogressive than in the case of FIG. 5.

FIG. 9 illustratesin the form of a block diagram a possible embodimentof a regulating device in which. the

signal from a. single detecting cell 12 may be used for ill regulatingthe rate of flow of the molten metal or the linear velocity of thesolidified bar. The cell 12 has one of its terminals grounded while theother one is connected by a wire 13 with the slider 14 of apotentiometer 15 the latter being connected across an electric cell 16.The resulting voltage (signal from the photo-electric cell minusadjustable voltage supplied by the potentiometer 15) is applied througha wire 17 to a synchronous chopper 18 actuated by the AC network. Thealternating voltage thus obtained is amplified in an amplifier 19 andthe am plified voltage is applied to the controlling phase of a maintwo-phase motor 20, the other phase of which is permanently energized bythe AC network. By properly adjusting the setting of the potentiometer15 it may be obtained that the voltage or potential of the wire 17 bezero when the level is normal, of one polarity when the level is highand of the other polarity when it is low. The chopper 18 energizes themain two-phase motor 20 in accordance for rotation in one direction orin the other, as this is well-known in the art, and the shaft 21 of thismotor may directly actuate the controlling member, as for instance therod and lever gearing 89 of FIG. 1.

It is finally to be observed that in the case of a plurality of cells(as for instance two), one could be used as a reference for modifyingthe conditions of the automatic regulation in accordance with externalinfluences, and more particularly with the variations in the temperatureof the molten metal. The reference cell may be arranged to see eitherthe bath Seven at its lowest level, or the jet- 3 itself, and theresulting signal may be added to or substracted from the signal from thedetecting cells. The reference cell may be disposed either in theoptical image, or behind another objective lens, as diagrammaticallyindicated in FIG. 10 wherein the reference cell 412 behind the auxiliarylens 21 is arranged to see the jet 3 as it issues from the tundish 2.

FIG. 11 shows a possible electric diagram in which the reference cell412 is connected across the above described potentiometer 15 of FIG. 9in lieu of the cell 16. It will be appreciated'that the counter-voltageapplied between the wires 13 and 17 thus varies in accordance with thetemperature of the jet and that it may be obtained that zero potentialon the wire 17 may always correspond exactly to the normal level line Aof FIG. 2 in spite of temperature variations.

It is to be understood that the term photo-electric cell should beunderstood lato sensu and that it should include any light-responsivedevice capable of emitting a signal in proportion to the intensity ofthe light received I claim:

1. A device to detect level variations with respect to a normal level ofthe upper surface of the liquid bath with in a mould for continuouscasting having an inlet with a substantially vertical axis tocontinuously receive a jet of molten metal and an outlet from which asolidified bar is continuously extracted, said device comprising opticalmeans completely exterior to said mould to form a optical image of theupper surface of said bath with an optical image of said jet flowingthereinto; and at least one de= tecting photo-electric cell. which issmall relative to the size of the image of the upper surface disposed ata small portion of said optical image of said surface, said photoelectric cell being situated far from the image of said jet, in suchmanner that said cell is responsive to level variations of the uppersurface of said bath within said mould above and below said normal levelwithout being sub stantially influenced by said jet itself.

2. In a device as claimed in claim 1, said optical means comprising anobjective lens having its axis obliquely disposed with respect to thevertical axis of the inlet of said mould.

3.. A device to detect level variations with respect to a normal levelof the upper surface of the liquid bath within av mould for continuouscasting having an inlet with a substantially vertical axis tocontinuously receive a jet of molten metal and an outlet from which asolidi= fied bar is continuously extracted, said device compris= ingoptical means completely exterior to said mould to form an optical imageof :the upper surface of said bath with an optical image of said jetflowing thereinto; at least one detecting photo-electric cell which issmall rela= tive to the size of the image of the upper surafce disposedat a small portion of said optical image of said surface, saidphoto-electric cell being situated far from the image of said jet, insuch manner that said cell is responsive to level variations of theupper surface of said bath within said mould above and below said normallevel without being substantially influenced by said jet itself; atleast one reference photo-electric cell so disposed that it isinfluenced by the general environment of said mould, but not by thevariations of the liquid bath level therein; and means to subtract analiquot portion of the rep sonse of said reference cell from theresponse of said detecting cell to reduce the influence of saidenvironment on said detecting cell:

5 4. In a device as claimed in claim 1, said optical means comprising anobjective lens having its axis obliquely dis posed with respect to thevertical. axis of the inlet of said mouldl References Cited UNITEDSTATES PATENTS 2,246,907 6/1941 Webster Normand- 22-473 23,306,07312/1942 Metcalf Wmmwmmwr, 250-238 10 $045,125 7/ 1962 Mason -s 250-2383,293,705 12/1966 Lenz et al, n s.. ..r 22--79 OTHER REFERENCES Athens:Temperature Compensation of Silicon Solar 15 Cells, IBM TechnicalDiclosure Bulletin, vol, 3, No. 10, March 1965, p. 65,

WALTER. STOLWEIN, Primary Examiner CL XR 20 73 290

